Hi...
I am using a standerd buck boost configuration. A inductor, diode(60EPF), capacitor and a MOSFET switch(IXFN80N50). The buck boost is designed so that it will handle 1.8KW power. All the rating of the component value has come through calculations and ensures that the converter will operate in continuous conduction mode.
During designing, I considered that the variation of the input voltage should be between 50-250 volt and output voltage should stay at 120 v. But I don?t have any control on the output and I also don?t need that for my purpose. I will be trying to track the maximum power of a wind turbine. All the algorithm will be done to a PIC 18F452 and it will generate the required PWM signal and thus switch the buck boost. Now PIC can only give us 0-5 volt. So,I used a driver stage(with TC 4420) to drive the MOSFEET which will give me 0-15 volt proportional to PIC signal. Driver and PIC has isolated ground with an optocoupler. Siganl from the driver is connected to the gate of MOSFET and ground of the driver connected to the source i.e. high side driving configuration.
The problem is :
Lets say, switching frequency is 100KHz and duty cycle is 50% from the PIC , so the driver stage ouput is 50% duty cycle with 0-15 volt voltage level and frequency is 100KHz to drive the MOSFET. Its ok. I have seen it.Now if I increase the input voltage level, say?10?20?30?gate signal ok?switching the MOSFET?getting output voltage.
But if I increase further?say?40?50?60?gate signal distorts i.e. it doesn?t show me 100Khz and so as the 50% duty cycle?gate signal just vanish after a certain input voltage...getting output voltage but that doesn?t make much sense.
I am stacked on this point and trying to search some literature but there is not much information about any practical solution. Waiting for any kind of suggestion.
Today i have bought IR2117 and IR2110 to use for a driver circuit. They have isolated ground and are useful for both high and low side driving. I have calculated my input driver circuit current to charge up the MOSFET GS cap and i have found that if a driver circuit can give me 6 amps then it will be ok. But in the data sheet of IR 2117 i didnt see any information about how much current it can give? It says Io+ 200/400mas..i am confused in this point too.
Will it be able to drive such high power level(around 2KW) MOSFET? I have seen that they are suitable but i need to be sure from someone or need to understand what does it mean?
A lot of questions but hope some former will guide me through the right way. I am stacked on this issue for along time.
Thanks Arif